In chemical plants, towers may be used to perform a process operation on a stream of gas and/or liquid. The process operation can include quenching, absorption, or stripping of one or more chemical components. When the stream leaving the process tower is in the gas phase, frequently a contacting device is installed to remove liquid entrainment from the exiting gas.
In a packed tower mist elimination is often achieved with the use of a contacting device comprised of glass-fiber material. Some such contacting devices are tall and cylindrical in shape and consequently referred to as “candles”. For example, in the sulfuric acid industry, liquid entrainment is commonly removed in sulfuric acid absorption towers and in drying towers using such candle filters.
The quantity of candles in a tower varies but can be up to fifty with candle heights of up to twenty feet. The candles are connected to a support within the tower. The support may be a plate known as a tubesheet. The candles are bolted either directly to the tubesheet, or are bolted to flanges which are raised up from the tubesheet. A gasket is typically placed between each candle and its supporting flange or tubesheet to ensure a good seal. Any leaks at this connection can significantly reduce the performance of the tower. The candles may either stand on or hang from the flanges or the tubesheet.
During installation, the candles are typically lowered into the top of the tower with a crane. They enter through one or more ports on the top of tower. FIG. 1 schematically illustrates a tower 10 with a candle 20 being installed therein according to the prior art. Tower 10 comprises a generally cylindrical housing 12 with a gas exit nozzle 14 located in an upper end thereof along the centerline 15 of housing 12. In the example illustrated in FIG. 1, a liquid outlet nozzle 2, gas inlet nozzle 5 with brick lining 4, packing support 6, packing 7 and distributor 8 are located in a lower portion of tower 10.
A candle installation port 16 is defined in the upper end of housing 12, located off centerline 15. Candle flanges 18 are located inside housing 12 at a plurality of locations for supporting candles 20. Flanges 18 may have gaskets (not shown) thereon for forming seals with candles 20. A candle 20 is suspended from a crane (not shown) by eyelet 21 and lowered through port 16 until it rests on flanges 18. Candle 20 is then manually shifted by workers (not shown), as indicated by reference numeral 20′, until candle 20 is in its final position, as indicated by reference numeral 20″. This process is reversed when candle 20 is removed.
The candle weights range from up to 500 pounds when dry and can increase to over 1500 pounds when wet after use. As one skilled in the art will appreciate, the weight and awkward shape of candles 20 makes it difficult to align candles 20 for bolting to the gaskets. Also, the manual shifting process may lead to damage of the candles, gaskets, or supporting flange or tubesheet. Furthermore, a gas-tight seal may not be realized between a candle and the flange or tubesheet if the candle is not properly aligned, or if any damage to the candle, gasket, flange or tubesheet has occurred. A damaged candle or ineffective seal results in poor tower performance characterized by high liquid entrainment in the gases exiting from nozzle 14.
Installation and removal of the heavy candles may also result in injuries to maintenance personnel. In addition to the increased weight, wet candles must sometimes be removed by specialized workers in cumbersome acid proof suits, since the environment inside tower 10 can be highly corrosive.
The size of the housing in which the candles are located is usually minimized for economic reasons. FIG. 1A illustrates an example arrangement of candles 20 within housing 12. The confined space adds to the difficulty of installing and removing the candles.
It is known to add extra candle installation ports to the housing of the tower in an attempt to make installation easier by reducing the distance by which the candles must be manually shifted. However, the extra installation ports add to the fabrication cost of the tower.
There exists a need for an improved method and apparatus for installation and removal of candles in and from towers.